U.S. patent number 4,258,292 [Application Number 06/034,455] was granted by the patent office on 1981-03-24 for flasher devices for lamps.
This patent grant is currently assigned to Tridon Limited. Invention is credited to Hillar Kassfeldt.
United States Patent |
4,258,292 |
Kassfeldt |
March 24, 1981 |
Flasher devices for lamps
Abstract
The invention provides a two-terminal flasher device,
particularly for flashing automobile lamps, that can replace the
thermal devices predominantly currently in use. An
electro-mechanical relay is used to flash the lamps, while an
electronic circuit controls the flashing rate. The power for
operating the relay and the electronic circuit is maintained by
means of a capacitor that is charged from the power source (the
battery) and then discharged while the power source is not
available, the electronic circuit being supplied from the capacitor
via a constant voltage source. Preferably the charging of the
capacitor is arranged so as to give an "instant-on" type of
operation. The lamp current is measured by a voltage measuring
means including a resistor formed by part of the copper of the
board on which the circuit is mounted, and the temperature
coefficient of the circuit is arranged to be as close as possible
to that of the copper. Upon detection of a lamp failure the
flashing rate is doubled by by-passing a divider in a timing chain
of the circuit. The current supplied to the relay coil is
controlled so that a relatively high closing current is supplied
initially to close the relay contacts; upon closure of the contacts
the relay current is lowered to a holding value (e.g. about one
fifth of the closing value) reducing the relay power consumption
and capacity required for the capacitor.
Inventors: |
Kassfeldt; Hillar (Burlington,
CA) |
Assignee: |
Tridon Limited (Burlington,
CA)
|
Family
ID: |
21876532 |
Appl.
No.: |
06/034,455 |
Filed: |
April 27, 1979 |
Current U.S.
Class: |
315/200A; 315/77;
340/331 |
Current CPC
Class: |
H05B
39/09 (20130101); B60Q 1/46 (20130101) |
Current International
Class: |
B60Q
1/46 (20060101); B60Q 1/26 (20060101); H05B
39/09 (20060101); H05B 39/00 (20060101); H05B
041/30 (); H05B 041/34 () |
Field of
Search: |
;315/2A,77,205,29R,227R,131,136 ;307/1LS ;340/641,642,81R,331 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Alfred E.
Assistant Examiner: O'Hare; Thomas P.
Attorney, Agent or Firm: Hirons, Rogers & Scott
Claims
I claim:
1. A flasher device for lamps and of the two-terminal type
comprising:
(a) first and second device terminals for connection respectively
to a power source and to a lamp to be flashed by the device;
(b) relay means having a pair of relay terminals that are connected
between the first and second device terminals for the passage of
lamp lighting current from the first to the second device
terminals; and
(c) electronic timing circuit means connected to the relay means
and determining the duty cycle period for which the relay terminals
are connected and disconnected upon closure of a lamp actuating
switch of a flasher circuit in which the flasher device is
connected;
(d) the device including a capacitor connected to the first device
terminal for supply of charging current thereto upon closure of the
lamp actuating switch and during an initial inhibit period of the
duty cycle period while the relay terminals are disconnected;
(e) the capacitor being connected to the relay means at the end of
the initial inhibit period for supply of holding current thereto
for holding the relay terminals connected after they have been
connected; and
(f) the capacitor being connected to the timing circuit means for
supply of operating current thereto at least while the relay
terminals are connected.
2. A device as claimed in claim 1, wherein the relay means is of a
type with which the operating current for connecting the relay
means terminals is greater than the operating current for
maintaining the terminals connected, and the circuit means includes
relay control means for controlling the relay operating current,
and detector means detecting the connection of the relay terminals
and causing operation of the relay control means to reduce the
operating current from the connecting value to the holding value
upon detection that the terminals are connected.
3. A device as claimed in claim 2, wherein the relay control means
is operative upon detection that the relay means terminals are
connected to maintain the relay means operating current at a
substantially constant holding value.
4. A device as claimed in claim 3, wherein the relay control means
maintains the relay means operating current at the said
substantially constant holding value by timed switching of the
power obtained from the capacitor.
5. A device as claimed in claim 2, wherein the said relay means is
an electromagnetic relay having a relay winding connected to the
said capacitor to be supplied with at least holding current
therefrom and having relay contacts that are connected closed and
disconnected open by movement of the relay armature.
6. A device as claimed in claim 1, wherein the timing circuit means
includes a constant voltage power supply means connected to the
capacitor to receive power therefrom at the voltage available
therefrom and connected to the remainder of the timing circuit
means to supply power thereto at a constant voltage.
7. A device as claimed in claim 1, and providing instant-on
flashing of the lamp to which it is connected, wherein the timing
circuit means includes;
relay control means for controlling the relay operating current,
and
timing means connected to the relay control means and preventing
feeding of closing current to the relay means during said initial
inhibit capacitor charging period of each lamp-on duty cycle
period.
8. A device as claimed in claim 7, wherein the timing circuit means
includes a single timing chain consisting of a frequency generator
and frequency dividers fed from the frequency generator, and
wherein a signal for determining the said initial inhibit capacitor
charging period is obtained from the frequency generator, and a
signal for determining the duty cycle of the device is obtained
from a subsequent frequency divider.
9. A device as claimed in claim 8, wherein the timing device
circuit means includes an AND gate through which the signals from
said signal generator and said subsequent frequency divider are fed
to the relay control means, so that the faster operating signal
from the frequency generator is ineffective during the lamp-off
duty cycle period.
10. A device as claimed in claim 1, wherein the said timing circuit
means includes voltage detector means connected between the device
terminals to detect the voltage therebetween, the voltage detector
means being connected to the relay control means and preventing
feeding of closing current to the relay means until the voltage has
reached a predetermined minimum value with corresponding charging
of the capacitor.
11. A device as claimed in claim 1, wherein the timing circuit
means includes means detecting the flow of lamp current between the
relay means terminals, and means responsive to detection of a
decrease in current corresponding to failure of a lamp to increase
the flashing rate by decreasing the duty cycle periods for which
the relay means terminals are connected and disconnected.
12. A device as claimed in claim 11, wherein the timing circuit
means includes a timing chain consisting of a frequency generator
and at least one frequency divider fed from the frequency
generator, and switch means connected to two different signal
outputs of the timing chain, the lamp current detecting means
controlling the switch means to supply the faster operating signal
from the respective output to the relay control means upon
detection of a decrease in lamp current corresponding to failure of
a lamp.
13. A device as claimed in claim 11, wherein the said means
detecting the flow of lamp current includes a resistor constituted
by part of the copper of a circuit board on which the timing means
circuit is mounted, and detector means connected across the
resistor and measuring the voltage drop produced by the current
passing therethrough.
Description
FIELD OF THE INVENTION
The present invention is concerned with improvements in or relating
to flasher devices for flashing one or more lamps such as are used,
for example, to control the flashing of vehicle lamps for hazard
warning and/or indicating a change in direction of the vehicle.
REVIEW OF THE PRIOR ART
Flasher devices of the so-called thermal type have been used
extensively in the automotive field, principally because of their
low cost coupled with an acceptable degree of reliability. However,
electronic devices have a number of advantages over the thermal
type, for example, they are generally more stable and reliable, the
same device can be used for both direction indication and hazard
warning, and it is possible to provide an indication of lamp outage
by increase of the lamp flashing rate. Therefore, a number of
attempts have been made to provide a flasher device in which the
flashing rate is controlled by an electronic circuit. The use of an
electronic circuit device to control the lamp current is generally
not economic at this time, owing to the large current to be
switched and the cost of solid state devices of the necessary
current rating, but this situation can of course change rapidly in
the future.
The standard thermal flasher device has only two terminals for its
connection into its lamp circuit, one for connection to the battery
and the other to the lamps to be flashed. The device may include a
third terminal for operation of a separate pilot light, but
nevertheless in the industry it will still be referred to as a
"two-terminal" device. The majority of automobiles presently
manufactured are wired to use a two-terminal device, and
consequently any attempt to market other than such a device is
inherently extremely difficult. The principal problem involved in
designing a two-terminal flasher device employing an electronic
circuit is that the device has a substantial voltage drop across it
only while its lamp controlling relay is open and the lamps unlit;
as soon as the relay closes its impedance decreases virtually to
zero and consequently so does the voltage across it. In fact it is
an industry requirement that the voltage drop introduced by the
flasher device while the lamps are lit is not more than 0.6 volt,
and this is too small to power any presently commercially economic
electronic circuit, bearing in mind that the product is highly cost
competitive; presently available inexpensive electronic circuits
require about 3 volts for their operation. Consequently a voltage
sufficient to operate the electronic circuit is only available
between the terminals while the lamps are not lit, and the absence
of power while the lamps are lit makes the device inoperable. This
difficulty does not exist if a third ground terminal is provided,
since the battery voltage is then always available between the
battery and ground terminals.
One attempt to provide a two-terminal electronic flasher device is
described in U.K. Pat. No. 1,383,826 of Philips Electronic and
Associated Industries Limited. The device described includes an
electromagnetic relay switch having a low-resistance holding
winding connected in series with the relay switch terminals between
the two device terminals, so that they will be connected in series
with the battery and the lamps to be flashed. A series combination
of a diode and a capacitor are also connected between the device
terminals in parallel with the holding winding and relay switch
terminals, and one end of a high resistance energising winding is
connected to the same terminal as the diode, while a multivibrator
is arranged to connect the other end of the energising winding to
one end or the other of the capacitor. Closure of the automobile
directional switch causes current to flow in the energising winding
to close the relay contacts and light the lamps; at this time the
capacitor is charging. When the relay contacts close, the current
through the energising winding ceases, but the relay is now held in
by the field of the holding winding through which the lamp current
passes. After a "lamp lit" period set by the multivibrator the
capacitor is connected by the multivibrator to supply current to
the energising winding, producing a field opposing that of the
holding winding sufficient to release the relay and extinguish the
lamps.
DEFINITION OF THE INVENTION
It is therefore an object of the invention to provide a new "two
terminal" flasher device for lamps, in which the flashing rate is
controlled by an electronic circuit.
It is another object to provide such a device with which the lamps
flash "instant-on" upon closure of the external directional
switch.
In accordance with the present invention there is provided a
flasher device for lamps and of the two-terminal type
comprising:
(a) first and second device terminals for connection respectively
to a power source and to a lamp to be flashed by the device;
(b) relay means having a pair of realy terminals that are connected
between the first and second device terminals for the passage of
lamp lighting current from the first to the second device
terminals; and
(c) electronic timing circuit means connected to the relay means
and determining the duty cycle period for which the relay terminals
are connected and disconnected upon closure of a lamp actuating
switch of a flasher circuit in which the flasher device is
connected;
(d) the device including a capacitor connected to the first device
terminal for supply of charging current thereto upon closure of the
lamp actuating switch during an initial inhibit period of the duty
cycle, and while the relay terminals are disconnected;
(e) the capacitor being connected to the relay means at the end of
the initial inhibit for supply of holding current thereto for
holding the relay terminals connected after they have been
connected; and
(f) the capacitor being connected to the timing circuit means for
supply of operating current thereto at least while the relay
terminals are connected.
DESCRIPTION OF THE DRAWINGS
A flasher device which is a particular preferred embodiment of the
invention will now be described, by way of example, with reference
to the accompanying diagrammatic drawings wherein:
FIG. 1 is a schematic circuit diagram of the device;
FIGS. 2 and 3 are different side elevations of the device itself to
show the physical arrangement of the principal components
thereof;
FIG. 4 is a graph showing the change with time of energising
voltage (solid line) applied to the relay coil and the resultant
current (broken line) through it, and
FIG. 5 is a graph of change of current with time, similar to FIG.
4, to illustrate a switching mode arrangement for supplying holding
current to the relay coil.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first particularly to FIGS. 2 and 3, a device of the
invention typically comprises an insulating base 10 on which is
mounted an electromagnetic relay 12 and a circuit board 14 enclosed
by a cylindrical casing 16. The base carries two device terminals
18 and 20 by which the device is connected respectively to a power
source, constituted with this embodiment by a 12 volt automotive
battery 22, and to the signal lamps 24 to be flashed. In FIG. 1 the
enclosure constituted by the base 10 and casing 16 is indicated by
a broken line 26. The base carries a third terminal 28 by which the
device is connected to a pilot light 30. The relay 12 has a single
high-impedance energising winding 32 (e.g. about 80-150 ohms) and
pairs of relay contacts 34 and 36 operated in known manner by the
relay armature, the latter pair controlling the flashing of the
pilot light 30. A capacitor 38 has one terminal connected to the
device terminal 18 via a diode 40 and the other terminal connected
to the device terminal 20. The flashing of the lamps 24 is
initiated by closure of the usual hand-operated directional
actuating switch 42.
Immediately upon closure of the switch 42 the capacitor 38 beings
to charge through the diode 40. The circuit components of the
electronic circuit are all supplied with operating current from a
constant voltage power supply 44 that maintains a constant output
of about 3 volts as long as a supply of 3 volts or more is fed to
it. The voltage fed to the circuit 44 reaches 3 volts almost
immediately and all of the electronic circuits then immediately are
active. The rate of flashing of the device is controlled by a
flashing rate module 46, which can be any known oscillator circuit.
This module generates a signal four times the required normal
flashing rate of about 90 per second, which signal is fed to a
chain of two flip-flop divider modules 48 and 50, so that a final
signal of the required normal rate is obtained (i.e. on and off
periods of about 330 milliseconds length) and is fed via a switch
52 directly to a low current relay control means or driver 54, and
via the switch 52 and an AND logic module 56 to a high current
controllable relay control means or driver 58.
The modules 46 and 50 are so arranged that their output signals are
at the beginning of the "lamp-on" part of the duty cycle when they
are switched on, the output from module 46 passing through inverter
60, and these signals are fed immediately to the AND module 56 and
relay control means 54. The "on" output signal from module 46 has a
duration of one eighth of 330 milliseconds namely about 42
milliseconds, and during this initial so-called "inhibit" period
the control means 54 is active and the control means 58 inactive,
whereupon a current of a value too low for the relay to close is
fed to the winding 32, while the capacitor charges. The driver 58
can only become active when the AND module 56 receives a signal at
all three of its inputs, two of which are from the switch 52 and
inverter 60, and the third of which is the output from a voltage
detector means 62. This detecter is connected between the terminals
18 and 20 and feeds an output to the AND module 56 when the voltage
at terminal 18 is at a predetermined minimum value, typically at
about 8 volts.
When all three of the required signals are fed to the AND module 56
the driver 58 is activated and feeds a much higher current to the
relay winding, sufficient to ensure its rapid closing. The length
of the inhibit period set by the module 46 is sufficient to ensure
that the capacitor will charge sufficiently for its subsequent
task, while the detector means 62 ensures that no attempt can be
made to close the relay until there is adequate voltage available
for the task. When the conditions are completely appropriate
therefore the relay closes positively. In a typical embodiment the
current provided by the driver 54 will be about 25 milliamps, while
that provided by the driver 58 is about 125 milliamps.
FIG. 4 is believed to show clearly this aspect of the operation of
the circuit, the solid line showing the value of the voltage
applied to the winding 32, while the broken line shows the value of
the corresponding current through the winding. Thus, during the
"inhibit" period of approximately 40 milliseconds a low voltage is
applied by the driver 54, and the current increases with the usual
exponential characteristic. At the end of the period the maximum
voltage, consisting of the battery voltage less the voltage drop
across the diode 40, is applied and the current increases to the
new higher relay closing value.
As soon as the contacts 34 close and the lamps 24 light the voltage
between terminals 18 and 20 falls drastically and the capacitor 38
begins to discharge through the relay winding 32, the charging path
being blocked by diode 40; the relay contacts close somewhat ahead
of the end of movement of the relay armature carrying the movable
contacts, and some of the current supplied by the discharging
capacitor will assist in completing this movement and must be
regarded as relay closing current. The detector means 62 detects
this voltage decrease between terminals 18 and 20 and its signal to
the AND module is no longer true, so that the relay control means
54 is active to reduce the voltage across the winding and the flow
of current therethrough to the lower values determined by the
control means, these values being ample to hold the relay in closed
condition. The control means 54 then maintains this holding current
substantially constant at the lower value, while the capacitor
discharges, decreasing considerably the amount of power required
from the capacitor. As mentioned above, in this specific embodiment
the holding current required is only about 25 milliamps instead of
the closing current of 125 milliamps, and the period during which
the high value closing current is applied is only about 20
milliseconds.
At the end of the "lamp on" duty period of about 330 milliseconds
set by the final flip-flop 52 the relay drive means 54 is made
inactive, reducing the relay holding current to zero whereupon the
relay contacts open to extinguish the lamps. It will be seen that
the AND module 54 ensures that the faster-operating signal from the
circuit 46 cannot now enable the high current control means 58
during the "lamp-out" period of the duty cycle, this period also
lasting about 330 milliseconds. The duty cycle then repeats. It
will be seen that this ability of the circuit to control the
current in the winding 32 reduces very considerably the size of the
capacitor 38 that is required, and follows from the fact that the
magnetic field required to hold the relay closed is considerably
less than that needed to close it, in this embodiment by a factor
of about five. The area below the broken current line in FIG. 4 is
representative of the power consumed by the relay of the invention,
while the chain dotted line shows the possible current flow in the
absence of this dual-level operation, which would follow the normal
exponential decay curve obtained as a capacitor discharges. The
shaded area therefore represents the decreases in power consumed.
In this specific embodiment it was found that the size of the
capacitor 38 could be decreased from about 1000 mfd to about 680
mfd.
It will be apparent that the invention will still provide a
substantial benefit if the relay holding current is simply reduced
to a lower holding value instead of to a constant value by a
constant current device, this lower holding value decreasing
progressively as the capacitor discharges. The arrangement must of
course be such that the decreasing holding current will not go
below the minimum holding value by the end of the lamp-on cycle
period, when the relay contacts must open.
It will be seen that with the circuit described the lamps are lit
about 40 milliseconds after closure of the switch 42, and to the
observer they will appear to light instantly; this "instant-on"
type of operation is highly desirable and fully justifies the added
expense represented by the voltage detector 62. The invention is
also applicable to a circuit with which the closure of the switch
42 is followed by the "lamp-out" part of the duty cycle, when the
voltage detector 62 will not be required, since the capacitor has a
complete half cycle of about 330 milliseconds to charge.
A device of the invention is further provided with a detector
resistor 64 which has a differential amplifier comparator module 66
connected across it, this module producing a signal that is fed to
the switch 52 to control it. The resistor 64 is traversed by the
current passing through the lamps and the voltage drop across it
will therefore depend upon the current drawn by the lamps. Upon
failure of one of the lamps the voltage applied to the amplifier 66
decreases; the resultant signal fed to the switch 52 actuates it to
shunt the flip-flop divider 50, so that instead the double-rate
signal from the flip-flop divider 48 is fed to the relay drive
means 54 and 58, whereupon the flashing rate is doubled to about
180 flashes per minute, indicating to the driver that a lamp is
out. This is a most desirable feature and is becoming an essential
requirement in many markets.
A further feature of this particular embodiment is that the
detector resistor 64 is formed from part of the copper of the
circuit board 14, so that a separate element is not required and
the resistor maintains a very uniform temperature balance with its
environment. The electronic circuit is then designed to have a
temperature coefficient as close as possible to that of the copper
of the board, so that temperature stabilization is more readily
achieved. In a particular embodiment the value of the resistor 64
is only 3.3 milliohms instead of a more usual value with prior art
circuits of about 10 milliohms, and the circuit element 66 is
sensitive to .+-.1 millivolt. A circuit employing four lamps 24
will produce a voltage of about 15 millivolts when any two lamps
are lit; it will be seen therefore that there is adequate
sensitivity to detect the failure of a single lamp. There is also
adequate sensitivity to detect the failure of one lamp in
three.
Although in this embodiment a single timing chain 46-50 is employed
and signals taken from different parts of the chain, it will be
apparent that separate timing circuits could equally well be
employed. Moreover, although for convenience in description and
clarity in explaining the operation of the invention the electronic
circuit is shown as comprising separate modules, it will be
understood by those skilled in the art that a number or all of
these modules may be combined together in a single integrated
circuit.
At the present state of the relay art an electromechanical relay is
still the most economical device for switching the large lamp
currents involved, and such a device inherently requires a smaller
holding current than closing current, but the invention is also
applicable to any other type of relay device in which the holding
current required can be less than the closing current. Such a relay
device may not employ moving contacts and for this reason in the
claims the relay terminals are referred to as connected and
disconnected, which correspond to the closed and open conditions
respectively of an electromechanical relay.
Reference is made to FIG. 5 to show an alternative switching mode
of operation of a single relay control module to obtain effectively
the required high closing current and the lower holding current. In
this switching mode the value of the current supplied to the relay
winding by the capacitor decreases exponentially with the usual
decay characteristic, and the single module is switched on for
progressively longer periods of time as the current available
decreases so that the required magnetic field is maintained in the
relay core until the end of the duty cycle period is reached. This
manner of achieving a constant average current is generally more
complex to implement but also is usually more efficient in
operation.
It will be seen that the invention provides a flasher device
employing an electronic timing circuit that is a completely
satisfactory replacement for the existing two terminal thermal
devices.
* * * * *